Koichi Hayashi’s research while affiliated with Japan Synchrotron Radiation Research Institute and other places

We performed X-ray fluorescence holography experiments in Sm-doped YbB6 with a boron cage structure to determine whether the difference of ionic radii of Sm³⁺ and Yb²⁺ affects the Yb lattice. We found that the intensity of the Yb atomic image around the doped Sm is in good agreement with the simulation. These results suggest that Sm doping does not cause fluctuations or distribution in the Yb lattice outside the boron cage because of the strong covalent bonds in the three-dimensional boron cage network. In contrast, the first nearest-neighbor (NN) Yb around Sm is shifted outward by approximately 0.2 Å from Sm, implying that the doped trivalent Sm pushes the first NN Yb out while maintaining a particular distance from Sm without fluctuation or distribution. Fullsize Image

X-ray fluorescence holography (XFH) was, for the first time, applied to a polycrystalline system in order to visualize local structures within a single grain in the system using an x-ray microbeam. XFH was performed on (Ba,Ca)(Zr,Ti)O3 (BCZT) piezoelectric ceramic as the polycrystalline system in the normal mode with a two-dimensional detector. After data acquisition and processing, we obtained a Zr-Kα hologram from the BCZT ceramic. The Kossel lines were clearly observed, which were in good agreement with our simulated results, although there is a possibility that the hologram is contaminated by the signals from other surrounding grains. Furthermore, we confirmed that several atomic images reconstructed from the obtained Zr-Kα hologram can be related to the Ti atoms around Zr in the real space plane. These results clearly demonstrate the applicability of XFH to polycrystalline samples, which significantly expands the potential use of this technique for micro- or mesoscopic research in materials science.

Three dimensional atomic structures of a zinc ferrite Franklinite ZnFe2O4 crystal were investigated by X-ray fluorescence holography with an atom-resolved and element-selected functions at room temperature. The obtained holograms were analyzed using a sparse modeling approach of a L1-regression. From the present experiment and analysis, it was found that Zn atoms are located at tetrahedral A sites, which is in good agreement with the existing X-ray diffraction data. On the other hand, well-damped atomic images are observed around the central Fe atom. The present results are discussed by comparing with existing neutron diffraction and X-ray absorption fine structure experiments, where cation exchange occurs between Zn and Fe atoms for fine particles by about 10–15%, but the existence of cation exchanges is not clarified by considering the positional fluctuations of the Fe atoms at the B sites. Fullsize Image

To tackle disorder in crystals and short- and intermediate-range order in amorphous materials, such as glass, we developed a carry-in diffractometer to utilise X-ray fluorescence holography (XFH) and anomalous X-ray scattering (AXS), facilitating element-specific analyses with atomic resolution using the wavelength tunability of a synchrotron X-ray source. Our diffractometer unifies XFH and AXS configurations to determine the crystal orientation via diffractometry. In particular, XFH was realised even for a crystal with blurred emission lines by a standing wave in a hologram, and high-throughput AXS with sufficient count statistics and energy resolution was achieved using three multi-array detectors with crystal analysers. These features increase tractable targets by XFH and AXS, which have novel functionalities.

Optimizing TiNb2O7 network for better battery performance In recent years, the need for safer and more efficient rechargeable batteries has grown due to the increasing use of renewable energy. Traditional lithium-ion batteries have safety risks, such as catching fire, especially when charged quickly. Researchers are exploring new materials to improve battery safety and performance. They studied a material called TiNb2O7, which could be a safer alternative for battery electrodes. Researchers prepared TiNb2O7 using different methods and tested its performance in batteries. They used advanced techniques to analyze the material’s structure at the atomic level. This study focused on how the arrangement of atoms affects the battery’s ability to store and release energy. The results showed TiNb2O7 has potential as a battery electrode, offering good capacity and safety. The study concluded that understanding the atomic structure can guide the development of better battery materials. This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author.

Zinc-anode batteries are known for their high capacity and safety; however, the formation of dendrites has been a concern due to their adverse effect on cycle performance. In this study, we focused on the initial formation of dendrites and performed in situ measurements using surface-sensitive grazing-incidence x-ray diffraction measurement to evaluate the atomic structure at the electrode/electrolyte interface. During the 1st charge, the zinc was deposited in an orientation close to that of the electrode; however, during the 2nd charge after the 1st discharge, it was observed that non-oriented precipitation occurred and that the surface irregularities expanded. During the discharge, it was observed that the zinc was rotating and melting, suggesting that the zinc concentration near the zinc surface decreases, making it easier to dissolve at the root of the initial dendrite than at the tip. Therefore, we suggest that future zinc-anode battery research should focus on additives that promote mass transport to dissolve the initial dendrites from their tips.

The local structure of a two-dimensional layered material, Bi2Rh3Se2, in which superconducting (SC) and charge-density wave (CDW) states coexist, was investigated using Bi Lα and Lγ X-ray fluorescence holography (XFH). The crystal of Bi2Rh3Se2 adopts a monoclinic lattice with a space group of C2/m (No. 12) at room temperature; however, the structure below the CDW transition (∼240 K) is still unclear because of the difficulty in analyzing single-crystal X-ray diffraction. Therefore, information on the crystal structure below 240 K is significant to fully investigate the relationship between the SC and CDW states. Precisely, the value of β has not been definitely determined, i.e., β ∼ 90° or ∼134° is still unclear. Therefore, the crystal structure above 240 K is still under discussion. In this study, we attempted to determine the crystal structure at 300 and 200 K by comparing the atomic images reconstructed from Bi Lγ holograms with images simulated based on crystal structure models. A Bi Lα hologram was also exploited to determine suitable atomic locations by comparison with the simulated ones. The atomic image simulated with the crystal structure of Bi2Rh3S2 below the structural phase transition temperature reproduced well the experimental atomic image at 200 K. Specifically, the line profiles of the reconstructed images at 300 and 200 K, which exactly reflect the intensity of the atomic spots, clearly indicate the structural variation above and below the CDW transition temperature, i.e., the supercell structure is suggested as the atomic location for Bi2Rh3Se2 below the CDW transition temperature.